Whisk egg whites until stiff, add half the sugar and whisk until dissolved. Fold in the rest of the sugar, vinegar, vanilla and cornflour.

Line the tray with foil and place mixture in centre of foil, smooth around with palette knife.

If using a gas oven, before starting to beat, mix, turn temperature up to the highest and when ready place tray into oven, turn down to the lowest point cook for about 1½ hours. Check if firm to touch, turn oven off and leave to cool in the oven gradually.